On Tue, 2018-07-10 at 16:55 +0200, Greg Kroah-Hartman wrote: > On Tue, Jul 10, 2018 at 09:44:33AM +1000, Benjamin Herrenschmidt wrote: > > On Sat, 2018-07-07 at 18:48 +0200, Greg Kroah-Hartman wrote: > > > No, kobject_get() should never happen on a 0 refcount object. That > > > being said, the code does allow it, so if things are messed up, it will > > > happen. I think that change happened when the switch to refcount_t > > > occured, before then we would WARN_ON() if that ever happened. I should > > > go fix that up, and restore that old behavior, so that syzbot starts > > > complaining loudly when stuff like that hits. > > > > > > So I hate using kobject_get_unless_zero(), and resisted ever adding it > > > to the tree as it shows a bad locking/tree situation as you point out > > > here. But for some reason, the block developers seemed to insist they > > > needed it, and so it is in the tree for them. I don't want it to spread > > > if at all possible, which makes me want to reject this patch as this > > > should be "a case that can never be hit". > > > > Except it can in that situation... at least unless you get my patch 2/2 > > (or the newer one I'm about to send that avoids adding a child counter > > and uses the one in kernfs instead). > > I like that fix, which should make this patch obsolete, right?
Yes, for that specific issue, but Linus seemed to think patch 1 was the "right thing to do" regardless... I suggest you read the backlog of thread if you are interested in the ins and outs of his position, we had a rather extensive discussion on this stuff. Cheers, Ben.
